The central theme of this Program is gene transfer to hematopoietic stem cells (HSC) or progenitor cells to correct genetic diseases affecting the production and/or function of blood cells. While the concept of gene therapy using HSC to provide safe and effective methods to treat congenital disorders has been under study for at least two decades, there have been only a few rare cases of successful clinical application. The techniques currently in use for gene transfer and expression in HSC are inadequate in most cases to yield clinical benefits. The goal of this Program is to investigate the mechanisms limiting successful clinical applications of gene transfer and to develop improved techniques which will broaden the range of diseases which may be treated effectively. The Project leaders have complementary expertise in the relevant areas of experimental hematology, immunology, signal transduction, and gene therapy and have a long-standing record of interactive collaborations. These advances can only be realized by combining each of these individual projects into a unified Program. This Program has five projects: 1. Transduction of human stem and progenitor cells, 2. Minimal Lentiviral Vectors for Gene Therapy of beta-thalassemia, 3. Optimized Gene Therapy for Human X-linked Agammaglobulinemia, 4. Gene Therapy for SCID due to Cytokine Receptor Defects, and 5. Gene Therapy for ADA-deficient SCID. Four Cores (Administrative, Cell Isolation and Analysis, Vectors and Animals) will support the projects with integrated services for optimal quality and efficiency. The information generated by these investigations will provide valuable knowledge to the field to increase the effectiveness of gene therapy interventions for hematologic disorders.